Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an image wise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant, which is dissolved in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. Commonly used carrier media include water, mixtures of water and organic co-solvents and high boiling organic solvents, such as hydrocarbons, esters, ketones, etc
Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from major deficiencies such as poor image stability against light and gases commonly contained in the air, such as ozone (O3), nitrogen oxide (NOx) and sulfur oxide (SOx), especially on receivers having porous ink receiving layers. One method of addressing these limitations is to use pigment-based inks. When designed properly, pigment based inks usually can demonstrate image stability significantly higher than the dye-based inks, and more importantly, approaching the archival quality as compared to silver halide photographic prints.
A major image quality drawback of pigment based inks is “differential gloss”, where the gloss of non-imaged areas is very different from that of imaged areas. One solution to this problem is to cover the entire receiver with a protective fluid as described in EP1057646 and EP1048466. However, this approach involves laying additional fluid over areas of a receiver already having inks deposited thereon. When an area of the receiver reaches its fluid absorbing capacity, adding additional fluids to the same area may lead to image artifacts such as inter-color bleed and mottling effect. Additionally, due to the drying time associated with ink and the large areas often requiring protective fluid, the overall print productivity can be significantly limited.
An object of the present invention is to use image-wise deposition of a gloss matching fluid in an ink jet printing system, applying the fluid only in non-imaged areas of an image. Furthermore, the composition of the fluid can be optimized based on physical properties affecting the gloss levels to achieve minimized gloss difference between imaged and non-imaged areas.